Supercritical fluid chromatography (SFC) and supercritical fluid extraction typically use highly compressible fluids, such as liquefied carbon dioxide (CO2) or other liquefied gases, as a carrier fluid within the systems. An example of a system utilizing the liquid CO2 flow in a fluid system is the high throughput purification system discussed in U.S. Pat. No. 6,309,541, which is incorporated herein by reference thereto. These liquefied gases are highly compressible, so they must be kept at low temperatures and high pressure when pumped to prevent cavitation in the fluid system. Systems utilizing liquid CO2 typically must maintain the liquid CO2 at approximately 0° C. or lower throughout the pumping process.
Pump assemblies have been developed that cool the pump head to help maintain the liquid CO2 in its chilled condition during the pumping process. Such pump assemblies typically utilize a variety of heat exchangers or thermoelectric cooling systems that mount on the outside of the pump assembly and cover the pump head. Other systems have utilized a recirculating cooling bath system that pumps chilled fluid through or around the pump head to chill the pump head. These pump designs, however, provide a significant amount of hardware and components that severely limit easy access to and serviceability of the pump head. As a result, maintenance of the pump head can require significant down time for the system during the routine maintenance or repair of the pump head or its components.
The process of pumping the liquid CO2 or other liquefied gas results in exposing the components of the pump assembly to very cold and harsh conditions. These conditions can significantly impact the accuracy or operational life of a pump assembly. Liquid CO2 pump assemblies encounter a further difficulty due to contaminants within the liquefied gas being pumped. These contaminants, when pumped through the pump head, can wear excessively on the pump head's valves and seals. In some situations, valves in pump heads must be serviced after only a short length of actual service time. Pump seals also often require servicing as a result of wear caused by contaminants in the liquefied gas. The conventional chilled pump assemblies that have limited access to the pump heads because of the chilling components are difficult to service quickly. As a result, the pump assemblies are often taken off-line for a significant period of time to perform the servicing or routine maintenance, thereby decreasing the actual operational time of the fluid system.